Marginal Adaptation of CAD-CAM Monolithic and Veneered-zirconia Crowns – Comparative Study

Objectives:
To evaluate marginal fit of monolithic lithium-disilicate-glass-ceramic (LDG) crowns; zirconia (ZR) copings veneered with 3 different techniques utilizing CEREC CAD-CAM system; and porcelain-fused-to-metal (PFM) copings veneered with feldspathic porcelain.
Methods: A molar tooth with porcelain crown preparation was used to make 25 identical replicas from epoxy resin. Replicas were divided into five equal groups (n=5). Five PFM crowns with laser-sintered copings constituted control group. There were four experimental groups: monolithic CAD/CAM LDG crowns (IPS-e.max-CAD, Ivoclar-vivadent); ZR core (IPS-e.max-ZirCAD, Ivoclar-vivadent) 0.5 mm thick veneered with hand-layered feldspathic porcelain (ZVL) (IPS-e.max-CERAM, Ivoclar-vivadent), ZR cores veneered with heat-pressed feldspathic porcelain (ZVP) ) (IPS-e.max-ZIR-PRESS, Ivoclar-vivadent) and CAD/CAM LDG fused-to-ZR cores (CAD-on) (IPS-e.max-CAD, Ivoclar-vivadent). Crowns were cemented to their respective dies with Panavia-F2 (Kuraray). Specimens were stored in water at 37 ^oC for one week then subjected to compressive cyclic-loading in Instron universal testing machine for 500,000 cycles between 50 and 450N. Specimens were then sectioned mesio-distally to measure marginal gap using SEM. Marginal gap was measured at 2 pre-assigned points per specimen. Data were statistically-analyzed using Karuskal Wallis test at 0.05 level of significance.
Results: Mean marginal gap in µ was 37.3(7.2) for LDG crowns while means for ZR crowns were: 39.4(16.70), 44.5(17.8) and 39.8(13.7) for ZVL, ZVP and CAD-on, respectively. For PFM crowns mean gap was 43.4(14.4). Karuskal Wallis test revealed no significant difference in mean marginal gap among groups (p=.64). Mean values of marginal fit of all four ceramic as well as PFM crowns were within the clinically-acceptable range (40 -100 µ).
Conclusions: Marginal gap measured with SEM of four types of porcelain crown did not differ significantly from those of PFM crowns.